Research has shown that multiple reproductive-age ruminant males reduce their forage intake substantially during the rut. Two hypotheses have been proposed to explain this rut-induced hypophagia phenomenon: the foraging-constraint hypothesis and energy-saving hypothesis. We compared the time budgets of different age-classes of male Siberian ibex Capra sibirica among different rutting stages to make clear what tactic was used by Siberian ibex. Focal animal sampling was used to collect behavior data from October to December in 2014, in the middle of Tianshan Mountains. We used Kruskal-Wallis tests and Spearman rank correlation tests to analyze behavior data. Our results show that the feeding time of both adult males and sub-adult males during the rut were substantially lower than that during the pre- and post-rut. However, the time spent lying was similar among different stages of the rut for both the adult and sub-adult males. The ratio of feeding time to lying time in the rut was also significantly decreased compared with pre-rut, and there is no differences were found with post-rut. The duration of rutting-related behaviors during the rut were considerably higher than the during pre- and post-rut, most of non-rut time was allocated to foraging for all males. The feeding time of females during the rut was lower than pre- and post-rut, the lying time during rut and post-rut were observably higher than during pre-rut. Our results show that the Siberian ibex males of different age-classes decrease their feeding time during rut. This rut-induced hypophagia could be mostly explained by the foraging-constraint hypothesis; while the energy-saving hypothesis could also contribute to the reduction of feeding time for Siberian ibex males in this season.